Peter stephanos director, office of material technology. Performance of mepdg dynamic modulus predictive models for. It is strongly encouraged this memo is read prior to downloading or viewing mechanistic. Nchrp project 1 42, topdown fatigue cracking of hotmix asphalt layers identify the mechanisms that govern the initiation and propagation of topdown fatigue cracking in hma layers, identify or develop methods of laboratory testing hma mixtures for determining susceptibility of the. Implementation of the nchrp 1 37a design guide final report volume 1. In the design guide, a predictive rutting system was developed to evaluate the permanent. Guidelines for implementing nchrp 1 37a me design procedures in ohio. National cooperative highway research program nchrp. Flexible pavement designs and performance predictions derived from the empirical 1993 aashto pavement design methodology and the mechanisticempirical nchrp project 1 37a approach are compared for a range of locations within the united states, each. The design guide developed under national cooperative highway research program nchrp 1 37a project is a very complex pavement analysis tool, with many input factors which characterize materials, climate, traffic and construction. There are several empirical models available to predict e. Evaluation of nchrp 7a rigid pavement design software. A global sensitivity analysis samples the entire input parameter space of selected input variables.
Pdf this study deals with the sensitivity of the nchrp 7a pavement design guide predictions to traffic data input. Aashto empirical versus nchrp project 7a mechanisticempirical. Traffic data required for each of the three hierarchical input levels. Better designs mean longer pavement life nchrp project 1. These brief case studies highlight how transportation agencies have put critical nchrp research results to use nationwide. Nchrp s novel coronavirus disease covid19 response. These samples are used to create a matrix of design scenarios which were then be run through the nchrp 1 37a design software, to predict pavement performance. The nchrp 1 37a and nchrp 1 40d models have been incorporated into the mepdg program to estimate e. In the mepdg, the responses generated by a single axle are evaluated at a series of predefined locations, and responses under multiple axle gears are determined using. The mechanisticempirical pavement design guide, related documentation, and the latest version of its software are available online for evaluation through 30 september 2011.
Dgit workshops and training mechanistic empirical design guide. Accurate determination of critical structure responses plays a vital role in the ability of the mechanisticempirical pavement design guide mepdg to achieve a reliable pavement design. These axle load spectra are a primary input to the mechanistic pavement structural response models. Pdf comparison of mechanisticempirical and empirical flexible. Nchrp 1 39 lrequired traffic loads are defined by the nchrp 1 37a project software lnchrp 1 39 supplies a more robust mechanism to enter that data l9 software converts traffic monitoring data into pavement design inputs. Trbs national cooperative highway research program nchrp synthesis 457. It is widely recognizedand specifically pointed out by the nchrp 1 37a project teamthat, for the distress models to be fully applicable for the particular materials, construction practices, and environmental conditions in a given state or geographic region, they should be calibrated with data obtained locally. Information about projects initiated subsequent to 1988 is available below. Pdf sensitivity of nchrp 7a pavement design to traffic input. The calibrated models in nchrp 1 37a software can be used by wsdot pavement specialists to better predict future pcc pavement performance. Because the mepdg procedure is so different from past, purely empirical procedures, agencies have found a need for training and assistance to implement and use it. Pccp models for rehabilitation and reconstruction decision. To account for the time dependency of hma, mepdg recommends calculation of the frequency of the applied load as a function of the vehicle speed and the pavement structure. This version will expire when the guide and software are available from aashto or at another time determined by nchrp.
Even at this reduced thickness, however, the predicted faulting for the shallow bedrock conditions is well below the design limit. Calibration of nchrp 7a software for the washington. Volume 1 summary of findings, implementation plan, and next steps. The design guide recommended by the project team in 2004 is based on mechanisticempirical me principles and is accompanied by software that handles the execution of the design and performance. Nchrp 1 37a level 3 inputs see table 535 for typical ranges and default values as functions of aashto and uscs soil class. Sensitivity analysis of longitudinal cracking on asphalt. The nchrp 1 37a design software takes all of these traffic inputs and computes the number of applications of each axle load magnitude by axle type single, tandem, tridem, quad and month. Background national cooperative highway research program nchrp project 1 37a, the largest in the over 40year history of the program, was recently concluded with the successful delivery of a recommended mechanisticempirical pavement design guide to nchrp by the research team of eres consultants, its subcontractors arizona state university and fugro consultants lp, and. Alternatives for calibration of dynamic modulus prediction. Background national cooperative highway research program nchrp project 1 37a, the largest in the over 40year history of the program, was recently concluded with the successful delivery of a recommended mechanisticempirical pavement design guide to nchrp by the research team of eres consultants, its subcontractors arizona state university and fugro consultants lp, and numerous individual. Implementation of the nchrp 7a design guide final report.
Accuracy of current complex modulus selection procedure. In 2004, nchrp 7a was completed and delivered a mechanisticempirical pavement design guide and accompanying software. Memorandum from aashto containing project scope and information. Sensitivity of the nchrp 1 37a pavement design guide, a global approach. The urgency of the situation necessitated its use, despite the lack of formal calibration guidance, some software bugs, and isolated model inconsistencies. Nchrp may revise this version as necessary and provide updates on the internet. The nchrp 1 37a software cannot model pcc thicknesses less than 7 inches. The results suggest that the default design criteria incorporated in the nchrp project 1 37a software are broadly consistent with what would be observed historically from pavements designed with the 1993 aashto guide. The products developed under nchrp 1 37a have provided advancements in pavement design practices and work is continuing under nchrp, fhwa and various state agencies. The software can be downloaded for installation on a local drive in. Nchrp 1 37a is highly interactive and integrally tied to the analysis of ac permanent deformation development under nchrp 919. New england verification of national cooperative highway. Ara has continued to improve upon the software developed under nchrp project 1 37a, and the current versionaashtoware pavement me designis available through aashto.
The nchrp 1 37a pavement design guide 2 characterizes traffic in terms of axle numbers by type and their load frequenc y dist ribution, i. The development of the mechanisticempirical pavement design guide mepdg under national cooperative highway research program nchrp projects 1 37a and 1 40d has significantly improved the ability of pavement designers to model and simulate the effects of. So when it came time for aashto to update its pavement design guidance to state dots, engineers needed a. The objectives of project 1 40d01 were to 1 work in coordination with the contractor for project 1 40d02 to produce improved, corrected versions 0. Summary of findings and implementation plan mdsha project no. The guide includes procedures for the analysis and design of new. The results suggest that the default design criteria incorporated in the nchrp project 1 37a software are broadly consistent with what would be observed historically from pavements designed with. Note that these values are for soils compacted at optimum moisture and density conditions. Mepdg provides significant potential benefits over the 1993 aashto guide. Following the direction of our parent organization the national academy of sciences, engineering, and medicine, the majority of our staff are working from home, until at least may 1. The mechanisticempirical pavement design guide mepdg the mechanisticempirical design guide for new and rehabilitated pavement structures 1, known as mepdg, was released in 2004 under the nchrp project 1 37a.
The contractor prepared a software specification that determines a critical minimum e value for hma based on projectspecific information on climate, traffic, pavement structure, and layer depth. Airfield and highway pavements specialty conference 2006. The software associated with nchrp project 1 37a was chosen as a promising tool worthy of assessment for this application. Information on all projects initiated under the nchrp from its inception in 1962 through 1988 is included in nchrp web document 7. Certain supporting technical reports from project 1 37a are available online in an unrestricted pdf format. Nchrp 1 37a models are able to be calibrated with some limited exceptions. Implementation of the aashto mechanisticempirical pavement design guide and software documents the experience of transportation agencies in the implementation of the 2008 american association of state highway and transportation officials aashto mechanisticempirical pavement design. Implementation of the nchrp 1 37a design guide final report volume 2. Special edition of summary of progress through 1988. Trends of pavement performance with reliability level were similar for both methodologies.
Design scenarios were then run through the 7a design software and. The objective of nchrp 7a is to develop a pavement design tool based on mechanisticempirical. Comparison of mechanisticempirical and empirical flexible. Among the variety of methods the national cooperative highway research program uses to showcase the value of nchrp research is a series of success stories titled impacts on practice. In 2004, nchrp 1 37a was completed and delivered a mechanisticempirical pavement design guide and accompanying software. Analysis of critical structure responses for flexible. It is strongly encouraged this memo is read prior to downloading or viewing mechanisticempirical design guide files andor. This report provides the details associated with these findings. The latin hypercube sampling lhs technique wu et al. This specification is based on a series of pavement design examples presolved with the pavement design guide software from project 1 37a. The mechanisticempirical pavement design guide mepdg is the research version of the newly released darwinme software by aashto. Sensitivity of nchrp 7a pavement design to traffic input. Pdf mechanisticempirical pavement design guide mepdg. The mechanisticempirical pavement design guide mepdg uses the complex modulus to simulate the time and temperature dependency of hotmix asphalt hma.
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